Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device, and more particularly, to an OLED display device for preventing a dark spot on the display device (i.e. a dead pixel).
Discussion of the Related Art
Recently, an OLED display device including an OLED is applied to televisions (TVs), monitors, mobile information devices, etc.
The OLED display device includes an OLED, which is configured with a white OLED (WOLED), and a plurality of color filters for realizing red (R), green (G), and blue (B). Also, a color filter on thin film transistor (COT) structure has been proposed where the plurality of color filters are disposed on a lower array substrate.
FIG. 1 is a circuit diagram of one pixel configuring a related art OLED display device. FIG. 2 is a plan view of an OLED display device having a COT structure.
Referring to FIG. 1, a pixel area P configuring the related art OLED display device includes a white OLED WOLED and a driving circuit unit 10 that drives the white OLED WOLED. The driving circuit unit 10 includes a switching thin film transistor (TFT) SW_Tr, a driving TFT DR_Tr, a sensing TFT SE_Tr, a capacitor Stg_C, and the white OLED WOLED.
The switching TFT SW_Tr is turned on according to a gate signal supplied through a scan line SCL and supplies a data voltage Vdata, supplied through a data line DL, to the driving TFT DR_Tr.
The driving TFT DR_Tr is turned on according to the data voltage Vdata supplied from the switching TFT SW_Tr, generates a data current from power VDD supplied through a power line VDL, and supplies the data current to the white OLED WOLED.
The sensing TFT SE_Tr is for sensing a threshold voltage deviation of the driving TFT DR_Tr that causes a degradation of image quality, and the threshold voltage deviation is sensed in a sensing mode. The sensing TFT SE_Tr supplies, as a sensing voltage Vref, a current of the driving TFT DR_Tr to a reference line RL in response to a sensing control signal Vsense supplied through a sensing line SEL.
The capacitor Stg_C holds the data voltage Vdata supplied to the driving TFT DR_Tr during one frame. To this end, the capacitor Stg_C is connected to a gate terminal and a source terminal of the driving TFT DR_Tr.
The white OLED WOLED emits light according to the data current supplied from the driving TFT DR_Tr.
The pixel area P includes the switching TFT SW_Tr, the driving TFT DR_Tr, the sensing TFT SE_Tr, the capacitor Stg_C, and the white OLED WOLED.
Referring to FIG. 2, the OLED display device having the COT structure includes a plurality of pixel areas P which are arranged as follows. Each of the plurality of pixel areas P includes a first area A1, which is disposed at one side (an upper side) of a corresponding pixel area P with respect to the scan line SCL crossing a space between adjacent sensing lines SEL, and a second area A2 which is disposed at the other side (a lower side). The first area A1 and the second area A2 are disposed between the adjacent sensing lines SEL. The white OLED WOLED is disposed in the first area A1, and the driving circuit unit 10 is disposed in the second area A2.
The driving circuit unit 10 is connected to the scan line SCL, the sensing line SEL, the data line DL, and the power line VDL which are adjacent thereto. The driving circuit unit 10 supplies the data current of the driving TFT DR_Tr to the white OLED WOLED through a connection line CL which is disposed in a third area A3 between the first area A1 and the second area A2.
The pixel area P includes a red pixel area P, a white pixel area P, a blue pixel area P, and a green pixel area P. The red pixel area P, the white pixel area P, the blue pixel area P, and the green pixel area P, as illustrated in FIG. 2, are disposed in order in first to fourth columns. In this case, a red color filter R is disposed in the red pixel area P, a blue color filter B is disposed in the blue pixel area P, and a green color filter G is disposed in the green pixel area P. Here, the red color filter R is disposed in the third area A3 where the scan line SCL is formed, in addition to the red pixel area P. The red color filter R disposed in the third area A3 prevents light from being leaked from a corresponding pixel area P.
FIG. 3 is a cross-sectional view of an area K illustrated in FIG. 2 and illustrates the third area A3 where a connection electrode CL is formed in the blue pixel area P. For reference, for convenience of a description, the scan line SCL is not illustrated in FIG. 3.
Referring to FIG. 3, in the blue pixel area P, the blue color filter B is disposed in the first area A1, and the red color filter R is disposed in the third area A3 which is separated by a specific interval from the blue color filter B. An overcoat layer OC and the connection electrode CL are stacked on the blue color filter B and the red color filter R. The connection electrode CL connects the driving TFT DR_Tr to an anode of the white OLED WOLED.
A method of manufacturing the OLED display device includes a plurality of thermal processes which are subsequent processes performed after a process of depositing a color filter. However, pigments of the red, green, and blue color filters R, G and B differ, and thus, the plurality of thermal processes have a difference in degree of thermal expansion. For this reason, in the related art OLED display device, since the blue color filter B is separated from the red color filter R in the third area A3, the connection electrode CL which is stacked on the blue color filter B and the red color filter R is broken. This is because the red, green, and blue color filters R, G and B are differently and repeatedly contracted and expanded in a thermal process after the red, green, and blue color filters R, G and B are deposited.
As described above, a problem where the connection electrode CL is broken occurs in the blue pixel area P and the red pixel area P and becomes a cause of a dark spot on the display (i.e. dead pixel).
In reference labels which are not described in FIG. 3, SUB refers to a substrate, GI refers to a gate insulation layer, and PAS refers to a passivation layer.